The present invention relates to a wound measuring method and apparatus for locating and roughly identifying a radioactive uranium and/or transuranium isotope deposited in a wound.
The use of radioactive isotopes is greatly increasing in many areas of science and technology so that a constantly increasing number of people is subject to the risk of accidents resulting in radioactively contaminated injuries. Of particular importance in this connection are long-lived, highly radiotoxic radionuclides which occur predominantly in industries which process nuclear fuels and in the reprocessing of nuclear fuels.
The number of accidents leading to contaminated wounds is relatively small compared to conventional injuries but these accidents do require particular medical attention because the resorption of radioactive material through opened lymph and blood vessels includes the danger of incorporation in, and thus damage to, the entire organism. This applies in particular for the long-lived and radiotoxic isotopes of the transuranium elements which are known to concentrate in bone tissue.
Detection of such radionuclides in a wound is possible only by measuring their radiation by means of suitable detectors since even quantities too small to be weighed constitute radiation-biological limit values.
The surgical procedure employed in the treatment of a contaminated injury depends on the type and extent of the injury as well as on the level, spread and type of radioactivity, and on the location of the deposit in the wound.
Problems are encountered in measuring the alpha radiation from the deposit in the wound since such radiation travels only a short distance, for example for plutonium 239 only about 40.mu. with an energy of 5 MeV, due to absorption of the radiation by tissue, wound secretion and coagulation.
Beta or gamma radiation is not difficult to measure since the absorption of such radiation in the body tissues is significantly lower. For that reason the low energy X-ray or gamma radiation occurring in alpha radiators is used to detect a radioactive deposit in a wound. This is disclosed in the periodical Strahlentherapie [Radiation Therapy] 146, 4 (1973), at pages 422-432.
In this known measuring process the low-energy X-ray and gamma radiation is measured by means of scintillation counters. A particular drawback thereof is that for structural reasons the detectors have such dimensions that the measurements can be effected only on the surface of the skin but not in the wound itself. The surgical procedure required to remove the radioactive deposit in the wound, however, must be substantially restricted in its spatial extent.
This presupposes that it is possible to locate the deposit in the wound as precisely as possible. The more imprecisely the location is determined, the greater must be the area of tissue operated on, in order to increase the chances of success, and this often includes otherwise unnecessary amputations. Thus, in the interest of maintaining the health and the full work capacity of the patient, it is urgently necessary to limit the surgical operation to the absolutely necessary area.
It has therefore been proposed, for example, in IEEE Trans. Nucl. Sci 19 (1972) No. 1; and IEEE Trans. Nucl. Sci 20 (1973) No. 1, to utilize semiconductor detectors for tissue measurements, i.e., measurements in the wound. However, semiconductor detectors are not suitable as means for precisely localizing a low energy emitting deposit in a wound because the temperature noise of the semiconductor detector in the range of the body temperature is so strong that it substantially masks the measured radiation signal. Moreover, since the probability that the semiconductor detector will produce a positive response is relatively low, i.e. there is a good likelihood that any given wound will not contain a deposit, measuring times in the order of magnitude of several minutes would be required. However, long measuring times are contrary to the requirement of giving the patient medical attention in the shortest possible time in order to avoid substantial damage.
Another drawback of semiconductor detectors is the relatively high operating voltage, of the order of magnitude of 1000 volts, which constitutes a potential danger from a medical point of view when used in the area of a wound.
It is also known, as disclosed in Phys. Med. Biol. vol. 16 (1971) No. 3, at pp. 397-404, from the field of nuclear medicine to use scintillation detectors to detect precisely known radioactive preparations which have been administered to the patient. The CsI (T1) crystal used for this purpose is, however, too insensitive for measuring low energy beta and gamma radiation. The collimator which is placed on the head of the probe would preclude use of the detector in a wound due to its diameter of 14 mm.